This invention relates generally to a projection-type display device, and more particularly to a colored projection-type display device using liquid crystal light valves.
Conventional projection-type display devices which use liquid crystal light valves such as those disclosed in Japanese Laid Open Application Nos. 179723/85, 35481/86 and 150487/86 separate the image to be displayed initially into its red, green and blue wavelengths of light. Each of these wavelengths of light is then directed toward a corresponding light valve which permits or prevents transmission of the light therethrough. The red, green and blue wavelengths of light which are permitted to pass through these light valves are synthesized by additive color mixing using dichroic mirrors, a dichroic mirror prism or the like. The synthesized image is then projected onto a screen through a projection lens.
Each of the light valves has a twisted nematic mode (hereinafter referred to as "TN" mode) of operation which is driven by an active switching array. Such light valves provide an image having a high resolution and a high contrast ratio and can be driven at a low voltage. Projection-type display devices using liquid crystal light valves ar also considered highly desirable due to their compact size and light weight as compared to conventional projection-type display devices using cathode ray tubes.
The photoelectric transfer characteristics of projection-type display devices using liquid crystal light valves during its TN mode of operation are dependent upon the wavelengths of light incident thereto. Due to such dependency, conventional projection-type display devices using liquid crystal light valves exhibit undesirable colorations in the gray scale, and poor color purity and reproducibility. The thickness of each liquid crystal cell is carefully monitored during manufacture. Cells with slight variations in thickness are discarded resulting in low yields and higher manufacturing costs.
Accordingly, it is desirable to provide a projection-type display using liquid crystal light valves which produce an image having excellent gray scale, color reproducibility and color purity as well as high resolution and contrast ratio. It is also desirable to provide a method for manufacturing the liquid crystal light values which produces higher yields and thus reduces the manufacturing costs.